Detectives have arrested a dual UK-Iranian national on suspicion of terrorism offences as part of an investigation into a suspected plot near RAF Fairford.
Counter-terrorism police said the 27-year-old man was arrested on Thursday in Westminster on suspicion of preparing terrorist acts under section 5 of the Terrorism Act 2006.
A second man, 26, who is a UK national, has been questioned under caution.
Five men in their 20s were arrested in the village of Whelford, Gloucestershire, outside the RAF base in the early hours of Sunday after police were alerted to suspicious vans in the area. They were released on police bail.
Announcing the most recent arrest, Vicki Evans, the senior national coordinator for counter-terrorism police, said: “As we’ve made clear, we’re looking at all possible angles – including possible foreign state involvement.”
Counter-terrorism police said searches of two properties had been undertaken in Westminster, London.
Evans added: “The investigation into circumstances surrounding events in Gloucestershire is hugely complex, and our specialist teams are interrogating multiple lines of inquiry.”
An Iranian link to the events in the Gloucestershire countryside over the weekend is considered increasingly likely, as the police and security services’ investigation continues. Senior US politicians, including the president, Donald Trump, have expressed surprise that the suspects were released on bail.
It was revealed on Sunday that a farmer driving home from a party at about 1am on Sunday had spotted the men and vans and called 999.
But on Tuesday it emerged that one of the five men arrested near the base called the police to report the incident.
The mounting view among investigators that Iran was likely involved was a key reason for Andy Burnham’s decision to call a meeting of Cobra, the government’s crisis committee, on Monday, which was attended by senior police and security officials.
Tensions have been high at RAF Fairford since Iran’s Revolutionary Guards said in July that the base was a legitimate target. Iran’s embassy in London has denied any involvement in the events of the past few days.
Ministers have been briefed that Iran has various reasons for hiring proxies, who sometimes are unwitting, to carry out acts that aim to eat up resources and create chaos.
The suspects were first arrested on explosives charges and then later for preparing acts of terrorism. The decision on Monday to bail the men came after an examination of what was found in the vans, and searches of addresses linked to them across London, all of which found no evidence of a viable device.
Counter-terrorism police are leading the investigation, which is trying to establish why the five men, all British nationals from London, were in the Gloucestershire countryside, close to a sensitive site in the middle of the night.
The vans were marked with the logo of a legitimate fuel transit company that later denied ownership of the vehicles.
People detained for terrorism offences can be detained under two legal schedules that dictate how long they can be held without charge.
Under the terrorism schedule, a suspect can be held for up to 14 days but cannot be bailed.
The 27-year-old man arrested on suspicion of preparing terrorist acts is being held under the Police and Criminal Evidence Act (Pace), a spokesperson for CTP said.
That means he could be released on bail under investigation, but detectives have much less time to hold him.
The five men arrested early on Sunday in the Gloucestershire countryside were held under Pace before being bailed the next day.
The Iranian embassy in London has said it “categorically rejects and strongly condemns the recent unfounded and malicious speculations” of Iranian involvement.
Eighty-five households were forced to decamp to a leisure centre on Sunday as the bomb squad and counter-terror police descended on Whelford.
Some of the evacuated residents were able to stay with families, about 60 people received support from a Cotswold district council rest centre in Cirencester, and 28 people were accommodated overnight in hotels.